WASHINGTON - President Barack Obama on Friday said the botched execution of a murderer in Oklahoma raises questions about the death penalty in the United States and he will ask the U.S. attorney general to look into the situation.

"What happened in Oklahoma is deeply troubling," he said.

The condemned man, Clayton Lockett, 38, who was convicted of murder, rape, kidnapping and robbery in a 1999 crime spree, died of an apparent heart attack minutes after the lethal injection protocol failed.

A prison report said the problem was largely due to a collapsed vein during the injection of the lethal drugs and that the needle was inserted in Lockett's groin instead of his arm.

Oklahoma's director of corrections called for a revision of the state's execution methods and a suspension of executions until new procedures are in place.

Obama cited uneven application of the death penalty in the United States, including racial bias and cases in which murder convictions were later overturned, as grounds for further study of the issue.

"And this situation in Oklahoma just highlights some of the significant problems," he said at a news conference.

"I'll be discussing with (Attorney General) Eric Holder and others to get me an analysis of what steps have been taken - not just in this particular instance but more broadly - in this area," he said.

"I think we do have to, as a society, ask ourselves some difficult and profound questions around these issues."

Oklahoma has sent Lockett's body to the Dallas County Medical Examiner's office for a complete post mortem examination, officials in the state said.

It was also testing a batch of drugs that was to be used in a second execution planned to come just after Lockett was put to death on Tuesday. The second inmate, convicted rapist and murderer Charles Warner, was granted a temporary stay due to problems with Lockett's execution.